Intervertebral disc injuries are painful, debilitating and costly to the patient. The intervertebral disc lies between the articular surfaces of adjacent vertebral bodies. The disc consists of concentric layers of collagen fibers, the annulus fibrosis, and the central nucleus pulposus, which it surrounds. The nucleus pulposus consists of a viscous fluid connective tissue matrix and cells. The cells of the nucleus pulposus, physaliphorous cells, are scattered in irregular aggregates throughout the extracellular matrix consisting of ground substance. On the exterior of the vertebrae, the annulus fibrosis and the vertebrae are supported peripherally by longitudinal ligaments that run the parallel to the spine.
The intervertebral disc functions in the manner of a hydraulic shock absorber with the nucleus pulposus acting as the hydraulic fluid. With advancing age, the collagen fibers of the annulus fibrosis becomes thinned and weakened. The nucleus pulposus may rupture through the annulus posteriorly and compress the nerve roots, a condition commonly known as a ‘slipped disc’. The discs implicated in cervical injuries are between the fifth and sixth (C5-C6) vertebrae and the sixth and seventh (C6-C7) vertebrae; and in lower back injuries, the fourth and fifth lumbar (L4-5) vertebrae or the fifth lumbar and first sacral (L5-S1) vertebrae are affected most often. In cases where the disc does not rupture, nerve compression may be caused by osteophyte formation from degenerative disc disease. The osteophyte protrudes into the intervertebral foramen and compresses the nerve root resulting in continuous or intermittent chronic pain.
When a surgeon removes all or part of a ruptured disc from the back, he enlarges the hole in the annulus fibrosis through which to remove the ruptured disc and loose disc tissue in the interspace. The formed hole never heals which allows the susceptibility of additional disc rupture though the persistent hole as well as an inflammatory cascade that results from exposure of the interior of the disc to the epidural space. Inflammation and fibrosis occurs in the intervertebral space, frequently resulting in changes in the surrounding tissues including the vertebrae, hyaline plates, dura mater and the spinal cord.
About 200,000 discectomies are performed every year. Biological repair of the annular hole or defect is essential to advance the standard of care of the patient with intervertebral disc injury. The present invention addresses this repair of the annular fibrosis by use of a cultured connective tissue construct that, when surgically applied to the defect in the annulus, closes the hole to form a barrier to prevent inflammation and additional disc rupture.